Simplified nitrogen cycle box model (IMAGE)
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The marine nitrogen cycle box model adapted from Kang et al. (2023), which considers two reservoirs: one containing organic nitrogen produced by diazotrophs and ammonium generated via remineralization (the fixer-ammonium reservoir, Nfixer/ammonium), and another including nitrate and organic nitrogen produced by nitrate-assimilating organisms (the assimilator-nitrate reservoir, Nassimilator/nitrate). The primary input flux to the marine nitrogen pool is nitrogen fixation (Ffix). Major output fluxes include water column denitrification (Fwcd) and sedimentary denitrification (Fsd), while only a small fraction of organic nitrogen originating from nitrogen fixation and nitrate assimilation is buried in sediments (Ffixer_burial and Fassimilator_burial). Internally, nitrogen is transferred from the fixer-ammonium reservoir to the assimilator-nitrate reservoir via remineralization (Fremin).
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